GADD153 is a mammalian gene whose expression is increased in response to a variety of stresses including DNA damage and growth arrest. It is a member of the CCAAT/enhancer-binding protein (C/EBP) family of transcriptional activators and may serve as a negative regulator of other C/EBPs. In this project, studies have focused on determining the regulation and function of GADD153 expression in response to diverse growth inhibitory and metabolic stimuli. Studies during the past year have concentrated on the induction in response to 1) glucose deprivation, 2) treatment with the growth inhibitory prostaglandin PGA2, and 3) during the acute phase response (APR). Previously, we had shown that glucose deprivation induces GADD153 mRNA expression in a reversible fashion. We have extended these studies to show that the GADD153 protein is similarly expressed and have characterized the response in detail. Induction of the gene is not due to lack of ATP as alternative energy sources (pyruvate) can not prevent the induction. C/EBPs have been implicated in the differentiation of adipocytes and GADD153 expression is also increased during this process. We have provided evidence, however, that GADD153 is not required for differentiation, but rather occurs as a result of glucose depletion due to the high rate of metabolism of the differentiating cells. 2) We have provided evidence that induction of GADD153 by PGA2 is mediated via elevations in intracellular calcium. PGA2 treatment results in an increase in intracellular calcium levels, and both this increase and the induction of GADD153 expression by PGA2 can be blocked by buffering intracellular calcium . 3) We have found that GADD153 is induced during the APR in rats following their injection with lipopolysaccharide. Induction of GADD153 is temporally delayed relative to that of other C/EBPS which also show elevated expression during the APR. We have provided evidence that C/EBP beta plays a role in regulating GADD153 expression.